In a typical cellular system, also referred to as a wireless communications network, wireless terminals, also known as mobile stations and/or User Equipment units (UES) communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to further evolve the UTRAN and GSM based radio access network technologies. In 3GPP, work regarding 3G Long Term Evolution (LTE) systems is ongoing.
Mobility management is an important function in maintaining cellular networks. The goal of mobility management is to track where cellular phones, or User Equipments (UEs), are located in order for mobile phone services to be provided to the various UEs included in any given network.
Each base station of a cellular network covers a limited geographical area, which may be referred to as a cell. Integrating the coverage of a number Of base stations, or cells, provides a cellular network with radio coverage over a much wider area. In E-UTRAN, an eNodeB or a group of these base stations may be referred to as covering a Tracking Area (TA). A Routing Area (RA) may be formed from one or more of these cells as well.
A Tracking Area Update (TAU) and/or a Routing Area Update (RAU) procedure allows a UE to inform the cellular network when the UE moves from one TA and/or RA to another. When an UE detects it has moved to a different TA and/or RA and the UE is not registered for that TA and/or RA, the UE will send a TAU and/or RAU request to the cellular network in order to get a Tracking Area Identity (TAI) and/or Routing Area Identity (RAI) list of TAs and/or RAs associated with the UE's current location.
The network node typically responsible for mobility management is the Mobility Management Entity (MME) in LTE systems and the Serving General Packet Radio Service Support Node (SGSN) in 2G/3G systems. The MME and SGSN are key control nodes typically responsible for idle mode UE tracking, paging procedures, bearer activation/deactivation processes, and the MME and SGSN are also responsible for choosing a Serving Gateway (SGW) for a particular UE.